In many fields, industrial installations are constituted by a plurality of components, such as, for example, tanks, heat exchangers, steam generators, pumps, which are connected together by pipes or tubes.
The components are arranged in buildings and are carried by vertical and/or horizontal support assemblies which are themselves fixed to the walls of the building, that is to say to the floor or the walls.
The positioning of the components relative to one another and also relative to the environment, that is to say relative to the walls of the building, is important both during installation of the components on an industrial site and during replacement of a worn component by a new component, in order that the connections between them can be made under the best conditions.
The general principles that are to be respected during replacement are that the new component must be integrated into the environment without questioning the original design, and the mechanical stresses caused by the replacement of the component must be minimised.
That is the case especially with the components of the loops of a primary circuit of a nuclear power station.
Pressurised water nuclear reactors comprise, inside a reactor building, a vessel which contains the core of the reactor and is filled with pressurised water, and a primary circuit constituted by a plurality of loops which communicate with the vessel by way of pipes. Each of the loops of the primary circuit is constituted by a plurality of components comprising, inter alia, a steam generator, in which the pressurised water is cooled and heats and vaporizes the feed water. The steam generators are arranged in areas called casemates, which are provided inside the reactor building.
Moreover, in addition to the steam generator, the casemate of each loop of the primary circuit also comprises a primary pump and the primary pipes allowing the vessel and the steam generator to be connected to the primary pump, as well as a pipe allowing the steam generator to be connected to the primary pump.
The various components of each primary loop, and more particularly the steam generator, the primary pump and the primary pipes, are connected to the walls of the building by support assemblies. The support assemblies are constituted, for example, by props or rings surrounding the component or by any other suitable member, which are fixed to the walls of the building by supports formed by plates. The supports are carried by adjustable joining members, such as, for example, tie rods.
When the building is constructed, the adjustable joining members of the supports are embedded in the walls and the floor and the positioning of each support has hitherto been carried out as follows.
First of all, a first layer of concrete, called the first-phase layer, is poured onto the walls and the floor and, when that layer has dried, the operators draw on the surfaces of the first layer check points for the positioning of the supports of each component. To that end, the operators find the coordinates of each check point in registers or on plans and determine the points on the corresponding surface with the aid of remote measuring devices, such as, for example, theodolites or tachymeters or laser scanning devices.
The operators then proceed as follows for each support.
They place the support on the corresponding joining elements and verify that the check points previously drawn on the surface of the first layer coincide with measuring points previously drawn on the support.
If the points do not correspond, the operators adjust the position of the support by adjusting each support point of the support longitudinally by means of the adjustable joining elements until the points coincide. The operators proceed in an analogous manner for each support of the component. A second layer of concrete, called the second-phase layer, is then poured at the determined location in order permanently to anchor the joining elements, and the position of the measuring points drawn on each support is verified again with the aid of the remote measuring devices.
The support assemblies are mounted on the supports and the corresponding component is then fixed to the support assemblies.
These various operations are obviously carried out for each component of each loop of the primary circuit.
This way of proceeding is long and tedious for the operators and the risks of error are not negligible owing to the large number of points to be determined and checked for each component which is associated with a plurality of supports, which means that the operators have to work for a considerable length of time in an environment which may be subjected to ionising radiation.
The coordinates of each point must be found and applied in the environment by operators, which multiplies the risks of incorrect transcription and of error.